The present invention relates in general to a heating apparatus for providing heat, light, and aesthetics to the interior of a structure, and the preferred embodiment of this heating apparatus is a vent-free, gas fireplace. More specifically, the present invention relates to a vent-free, gas fireplace which is equipped with a catalytic converter for secondary combustion of the primary combustion exhaust or emissions.
The use of a catalytic converter for a vent-free fireplace is known in the art as disclosed by U.S. Pat. No. 5,678,534 which issued Oct. 21, 1997 to Fleming. One purpose of the catalytic converter is to ensure that most of the unburned hydrocarbons and/or carbon monoxide, the by-products of the primary combustion, are converted to carbon dioxide and water. This enables the emissions from the catalytic converter to be exhausted directly into the room of the structure where the fireplace is positioned. By converting the unburned hydrocarbons and/or carbon monoxide to carbon dioxide and water, the emissions are not harmful and the fireplace does not need to vent any of the emissions to the outside atmosphere, thus enabling a vent-free fireplace design. As will be explained with regard to the present invention, the characteristics of its primary combustion are such that the by-products of that primary combustion meet, from a safety standpoint, the applicable standards, allowing these combustion by-products to be exhausted directly in to the room of the structure where the fireplace is positioned.
To the extent the '534 Fleming patent represents traditional thinking, it is seen that such traditional thinking includes a separate air pathway in the primary combustion chamber. Air pathway (14) of the '534 Fleming patent is provided behind a reflective sheet for helping to control the temperature of the reflective sheet and reduce heat transfer from the vicinity of the reflective sheet (11) rearwardly of the heater. The configuration of the firebox relative to the outer casing and the placement of the reflective sheet create three air convection pathways. Ultimately all three are mixed prior to being exhausted out into the room through outlet (10). Two of the corresponding flow paths are directed to the uppermost portion of the firebox and into the catalytic converter. As such, the separate air pathway (14) created in part by the reflective sheet, is used in part to provide a source of supplemental oxygen or air to the catalytic converter.
The creation of a separate air pathway for a supply of oxygen or air to the catalytic converter requires at least one additional component to be incorporated into the overall assembly. Whether this additional component is a reflective sheet or some other partitioning panel, its addition represents an added complexity and added cost to the corresponding heating apparatus (i.e., fireplace). The partitioning created by this reflective sheet also reduces the size of the combustion chamber volume for a given firebox size. This is believed to have a negative effect on primary combustion, necessitating the secondary flow of air (oxygen) for the catalytic converter. It would therefore be a design improvement if the construction complexity of the fireplace, as depicted by the Fleming patent, could be simplified without sacrificing the cleanliness of the emissions from the combustion chamber so that these emissions could be safely exhausted directly into the room of the structure. Such an improvement is provided by the present invention as briefly described below and as explained in greater detail in the description of the preferred embodiment.
With reference to the structure of the present invention, it will be understood that during the combustion process, outside (room) air flows into the primary combustion chamber where a gas burner is located. This flow pattern is due simply to the natural phenomenon of thermal buoyancy, i.e., warm air rises. This same air flow phenomenon is used to route an incoming flow of air into an outer air chamber (i.e., blanket) which surrounds the combustion chamber. By the proper balancing of the flow of fresh air in and exhaust air out from the primary combustion chamber, it is possible to attain and maintain a self-sustaining combustion process through the catalytic converter which is used in the present invention. In part, this combustion result is achieved by eliminating any secondary pathway within the primary combustion chamber and by isolating the flow of cooling air in the outer chamber from the primary combustion chamber.
As the hot air from the primary combustion process rises and draws in more combustion air, the rate of incoming flow is influenced in part by the temperature of the exiting air flow (post-combustion). By not mixing the second flow path of cooling air with the combustion emissions, sufficient air is drawn into the primary combustion chamber and into the catalytic converter for the combustion needs and in order to sustain the combustion process through the catalytic converter. This absence or lack of any mixing of the air flows is in sharp contrast to the teachings and structure of Fleming which mixes the air flows which are prior to or upstream of the catalytic converter. There is also mixing of the flow streams after or downstream of the catalytic converter. The mixing of these flows was the focus of arguments advanced in support of the patentability of the Fleming device.